The present invention relates in general to a hobbing machine for manufacturing spur- and worm gears, and in particular to a hobbing machine of the type which has a tool-supporting stand on which is arranged a hob carriage movable parallel to the axis of the workpiece and supporting a swivel head which in turn supports a slide movable in tangential direction relative to the workpiece; the machine further includes a differential gear system which is coupled with a hob driving gear system.
Prior-art hobbing machines for manufacturing spur gears and worm gears which have a separate feed drive branched off for driving both the axial and tangential feed drive elements, are known, the feed drive being coupled to the hob-driving gears via a differential gear system. Such a prior-art machine is described for example in the German patent application No. DD-WP 134 926 and is designed in such a manner that the indexing and differential change gears and the differential system are arranged in the machine stand at the side thereof facing the hob carriage and the drive elements in the branches of the feed drive system for the axial and tangential drives are arranged immediately in the hob carriage. A gear train connection leads from the branch of the feed drive in the hob carriage and is coupled via differential change gears for the differential system in the stand and therefrom a part of the hob driving gears is coupled via indexing change gears to the workpiece clamping table and another part of the hob driving gears is connected to the tool.
Even if by means of this known arrangement employing a branch of the feed driving gears in a hob carriage for the axial and tangential feed results in a very short gear trains having respectively a small number of gear elements the location of the differential system and of the differential and indexing change gears in the machine stand still produces several substantial disadvantages.
One of these disadvantages is the fact that relatively long parts are necessary in respective gear trains. As a consequence, the rigidity of the gear system and thus the attainable accuracy of the resulting product is negatively influenced. In addition, in order to install the gear elements in the machine stand there are needed gear boxes which in turn require large openings and spaces in this important component part of the machine. As a result, apart from increased costs for material and machining work, the stability of the machine tool is adversely affected. Moreover, due to the widely separated arrangement of the differential and indexing change gears and of the branch gears of the feed drive no central servicing is possible.